The present invention relates to the field of mass-storage devices. More particularly, this invention relates to a method and apparatus for reducing and/or isolating actuator and other internal noise from disc drives.
Devices that store data are key components of any computer system. Computer systems have many different types of devices where data can be stored. One common device for storing massive amounts of computer data is a disc drive. The basic parts of a disc drive are a disc assembly having at least one disc that is rotated, an actuator that moves a transducer to various locations over the rotating disc, circuitry that is used to write and/or read data to and from the disc via the transducer, and a bus interface to connect the disc drive into an information-handling system. The disc drive also includes circuitry for encoding data so that it can be successfully retrieved from and written to the disc surface. A microprocessor controls most of the operations of the disc drive, in addition to passing the data back to the requesting computer and receiving data from a requesting computer for storing to the disc.
The disc drive includes a transducer head for writing data onto circular or spiral tracks in a magnetic layer the disc surfaces and for reading the data from the magnetic layer. In some drives, the transducer includes an electrically driven coil (or xe2x80x9cwrite headxe2x80x9d) that provides a magnetic field for writing data, and a magneto-resistive (MR) element (or xe2x80x9cread headxe2x80x9d) that detects changes in the magnetic field along the tracks for reading data.
The transducer is typically placed on a small ceramic block, also referred to as a slider, that is aerodynamically designed so that it flies over the disc. The slider is passed over the disc in a transducing relationship with the disc. Most sliders have an air-bearing surface (xe2x80x9cABSxe2x80x9d) which includes rails and a cavity between the rails. When the disc rotates, air is dragged between the rails and the disc surface causing pressure, which forces the head away from the disc. At the same time, the air rushing past the cavity or depression in the air bearing surface produces a negative pressure area. The negative pressure or suction counteracts the pressure produced at the rails. The slider is also attached to a load spring which produces a force on the slider directed toward the disc surface. The various forces equilibrate so the slider flies over the surface of the disc at a particular desired fly height. The fly height is the distance between the disc surface and the transducing head, which is typically the thickness of the air lubrication film. This film eliminates the friction and resulting wear that would occur if the transducing head and disc were in mechanical contact during disc rotation. In some disc drives, the slider passes through a layer of lubricant rather than flying over the surface of the disc.
Information representative of data is stored on the surface of the storage disc. Disc-drive systems read and write information stored on tracks on storage discs. Transducers, in the form of read/write heads attached to the sliders, located on both sides of the storage disc, read and write information on the storage discs when the transducers are accurately positioned over one of the designated tracks on the surface of the storage disc. In some disc drives, the tracks are a multiplicity of concentric circular tracks. In other disc drives, a continuous spiral is one track on one side of a disc drive. Servo feedback information written on the disc(s) is used to accurately locate the transducer.
The transducer is also said to be moved to a xe2x80x9ctarget track.xe2x80x9d Once the storage disc spins and the read/write head is accurately positioned above a target track, the read/write head can store data onto a track by writing information representative of data onto the storage disc. Similarly, reading data on a storage disc is accomplished by positioning the read/write head above a target track and reading the stored material on the storage disc. To write on or read from different tracks, the read/write head is moved radially across the tracks to a selected target track in an operation called a xe2x80x9cseek.xe2x80x9d A seek is movement of an actuator assembly from a first track to a second target track. Acoustic emissions are more prevalent during rapid disc seek operations. To perform a seek, the actuator assembly is moved to the required position and held very accurately during a read or write operation using the servo information.
Typically, current is applied to an electromagnetic rotary motor in the actuator, causing the actuator assembly to rotate rapidly relative to the disc-drive enclosure. There is a quick rotational impulse transmitted to the disc drive case as the actuator is accelerated, and another quick rotational impulse in the opposite direction transmitted to the disc drive case as the actuator is decelerated. That is, the rotary acceleration of the actuator causes a rotary acceleration of the case in the opposite direction. These and other mechanical vibrations are radiated from the disc drive case as acoustic noise.
The detrimental impact of high acoustic emissions from disc drives is well known. Acoustic noise emissions from computer fans and disc drives result in an unpleasant workplace environment, particularly when many disc drives are concentrated in one area. The xe2x80x9cplinkxe2x80x9d or xe2x80x9ctickxe2x80x9d sound from each of numerous seek operations of numerous disc drives, though each is individually small, adds up to a large overall noise problem for large installations. The acoustic noise may also be absorbed by neighboring disc drives, possibly causing errors in those drives due to increased vibration levels. Government agencies in many countries are now requiring that the average level of sound energy from office equipment be substantially reduced. Computer manufacturers are also placing acoustic-emission standards on disc drive manufacturers. Manufacturers of disc drives also recognize that certain performance improvements for disc drives, namely increased disc rotational velocity and increased actuator speed and frequency, contribute to unwanted acoustic noise. Because many environments where disc drives are used are sensitive to the amount of acoustic emissions (or noise) coming from an operating disc drive, it is therefore desirable to reduce such acoustic noise.
Several methods to reduce the intensity of unwanted acoustic noise have been attempted. Among the several methods are the use of external dampening techniques for the entire disc drive. For example, mechanically isolating the cover of a disc drive from the mechanical reinforcement structure with a continuous airspace. Some of the unwanted acoustic noise emanate from a xe2x80x9cdrum-likexe2x80x9d top cover and from the base plate of the disc drive. Some improvements have been made addressing the acoustic noise that escape from the top cover, for example using cover dampers and adhesives with inherent dampening properties between the base and the cover.
Other attempts try to isolate the actuator from the disc-drive case in order to reduce the unwanted acoustic emissions during disc seeks. Such actuator isolation conventionally includes using plastic and rubber mounts on the pivot bearing assembly of the actuator. Some attempts have either centered on dampening the acoustic energy already in a disc base plate by placing foam between a printed circuit board and the base plate, or on decoupling the spindle and actuator mechanism from its enclosure by using a plurality of rubber isolator mounts. Other attempts include moving the actuator with less force to reduce impulse forces and thus reduce large acoustic spikes, however this can increase the time needed to complete the seek. Nevertheless, each of these improvements have proved marginal, and some have been prohibitively costly. There is a need for a method and apparatus to substantially reduce unwanted acoustic emissions from the disc drive due to the actuator seeks and disc rotation. There is also a need for a method and apparatus to reduce the amount of vibration and shock absorbed into the disc drive from the external environment. There is also a need for an inexpensive method and apparatus.
A method and apparatus is described for reducing and isolating actuator noise in disc drives. An isolation mount is provided between the disc-drive case and its external mounting assembly. In some embodiments, the isolation mount includes a soft mount that provides a vibration- and noise-dampening function for relatively small movements (in some embodiments, the isolation mount is designed very xe2x80x9csoftxe2x80x9d in order to produce a natural frequency of less than about 100 Hz about the center of mass; in other embodiments, the design is for a natural frequency of less than about 300 Hz) and a stiffer mount that provides a shock-isolation function for relatively large movements. In some embodiments, the isolation mount allows the disc drive to rotate somewhat freely about its center of gravity, in order to reduce the acoustic energy emitted or transferred to the external mounting assembly by an actuator seek.
Most generally, a disc drive system includes a disc case having a base plate, a rotatable disc and an actuator mounted to the base plate, and a cover. The disc case is held to an external mount. A transducer is mounted to the actuator in transducing relation to the disc. The disc case is acoustically isolated from the mount.
One aspect of the present invention provides a disc drive that includes an external mounting member, a disc case, and an actuator assembly mounted within the disc case. The actuator assembly has a shaft, the shaft having a rotational axis. The disc drive also includes at least one damper (a structure that dampens sound and/or vibration) holding the disc case to the external mounting member that allows rotational movement of the disc case relative to the external mounting member in order to reduce the emission of sound from the disc case.
Another aspect of the present invention provides a disc drive that includes an external mounting member, a disc case, an actuator assembly mounted within the disc case, and at least one damper holding the disc case to the external mounting member, the damper including a softer part and a stiffer part, wherein the softer part acts primarily for relatively small movements of the disc case and the stiffer part acts primarily for relatively large movements of the disc case.
Yet another aspect of the present invention provides a method for reducing vibrations of an actuator assembly entering a case of a disc drive. The method includes allowing more rotational movement of the case within a frame than is allowed of another mode of movement, and dampening rotational vibrations of the case.